Balancing apparatus for slide valves of compressors



G. FORNACA Oct. 1, 1929.

BALANCING APPARATUS FOR SLIDE VALVES 0F COMPRESSORS Filed NOV. 1].. 1.926

Patented Get. 1, 1929 ear GUIDO FORNACA, OF TURIN, ITALY Application filed November 11, 1926, Serial No. M1768, and in Italy November 17, 1925.

This invention relates to an apparatus for balancing the inertia forces produced by reciprocating slide valves of air pumps and compressors of internal combustion engines whereby the stresses and the wear of the driving members are considerably reduced.

The reciprocating slide valves are generally balanced with respect to the fluid pressure acting on them, so that the external stresses to which they are subjected are reduced to their dead load and to the inertia forces.

The dead load is nearly always negligible,

when, however, on account of the size of the machine to which they are applied, said slide valves have a considerable size and a quick motion, the inertia forces acquire very high values, so that the driving membersmust be of a large size and are subjected to a rapid wear.

The balancing apparatus forming the object of this. invention is characterized by the fact that the balance is obtained by coupling the slide valve with a double-acting piston movable in an air-tight cylinder in which air is compressed, thereby producing a resistance which compensates the inertia forces.

The accompanying drawing shows by way of example a constructional form of the object of this invention in connection with an air pump.

The air compressor 10 is provided with a cylinder 11 in which reciprocates the compressor piston 12. The cylinder 11 is provided with ports 13 and 14 connecting the casing 15 in which recipr-ocates the hollow cylindrical slide valve 16. A portion of the casing 15 is formed into a balancing cylinder 17 closed at one end and having at the center an opening 18 in its side wall connected by a pipe line 19 to the compressed air outlet 20. Within this balancing cylinder 17 reciprocates the small balancing piston 21 which is connected to slide valve 16 by rod 22 passing into the cylinder so that the slide valve 16 and the small balancing piston 21 reciprocate together. When the compressor piston 12 is in the position illustrated, namely, descending, air at atmosphericpressure will enter through port 23, pass upwardly through the hollow slide valve 16 and then through port 13 to the space in cylinder 11 above the piston 12. The compressor piston 12 as it descends compresses the air beneath it, forcing it outwardly throughport 14 around the contractedsectionof the slide valve 16 to the outlet 20. At the descending movement of compressor piston 12 the slide valve 16 with its balancing piston 21 will ascend. The operation described above is reversed as the compressor piston 12 ascends, thus making a (1011- ble acting compressor,

By virtue of the slide valve motion the inertia forces will be directed upwards during the upper half of thestroke of the slide valve and downwards during the lower half; on the contrary the pressure on the piston 12 is directed downwards during the upper half and upwards during the lower half of the stroke; it will therefore be sufficient to suitably proportion the, piston area and the volume of the cylinder dead spaces to the weight and speed of the slide valve in order to obtain a balance between the pressure and inertia forces, thus fully unloading the driving members.

When it is necessary to balance the dead load. of the slide valve itself as well, it will be suflicient to create a hi her pressure in the lower cylinder chamber, this being easily obtained by placing the suction openings in a higher position.

The above described apparatus gives perfectly satisfactory results with a constant angular speed of the engine. But when said speed is variable, and as the pressure in the 35 cylinder remains constant or undergoes only slight variationsas the angular speed of the engine varies, while the inertia forces vary according to the square of the speed itself, there would be no permanent balance between the pressure and the inertia forces.

In the particular case of two cycle engines which are provided with an air pump for scavenging the cylinders, it will be possible to obviate this drawback by feeding the balancing cylinder with pressure air from the pump itself, instead of with air at the atmospheric pressure; it is well known in fact that the scavenging air pressure rises as the number of turns of the engine increases; the pressure on the balancing piston will rise in the same manner and said rise of pressure Wlll within certain limits be such as to allow for the increase of the inertia forces and to reestablish the balance between the inertia forces and the pressure.

To create a changeable balance between the pressure on the piston 12 and the inertia forces the balancing cylinder 17 is fed through pipe 19 connected to the outlet 20 with air under pressure from the compressor, the m nt depending upon the ang speed of the engine.

What I claim is:

1.. In an air compressor for an internal combustion engine, the combination of a slide valve, a balancing cylinder, a balancing piston within said cylinder reciprocable with said slide valve, and means for varying the pressure within said balancing cylinder in accordance with the varying speeds of the engine to, balance the inertia forces produced by said slide valve.

2. In an air compressor for an internal combustion engine, the combination of a slide valve, a balancing cylinder, a balancing piston within the said cylinder connected to said slide valve, and a direct connection between the pressure supply created by the compressor and said balancing cylinder so that the pressure within said balancing cylinder will be varied in accordance with the varying speeds of the, engine to balance the inertia forces produced by the slide valve.

In testimony that I claim the foregoing as my invention I have signed In name,

e lino hoRNAGA. 

